The present invention relates to a vibration wave motor driven by a travelling wave, and more particularly relates to a motor structure for increasing the output torque.
Japanese Laid-open Patent Publication No. 61-277384 published on Dec. 8, 1986 discloses a vibration wave motor. FIG. 6 is a cross-sectional view of such a conventional vibration wave motor.
Referring now to FIG. 6, the conventional wave motor is explained. A stator (13) is fixed to a housing (11) by a support plate (10). A rotor (12) is fixed to a spindle (6) by a support plate (9). The spindle (6) is rotatably supported by bearings (7) which are fixed to the housing (11). The stator (13) is comprised of an intermediate elastic member (3), a pair of ring-shaped piezoelectric members (2a, 2b) and a pair of elastic members (1a, 1b). The piezoelectric member (2a) and the elastic member (1a) are stacked and adhered onto one side of the intermediate elastic member (3). Further, the piezoelectric member (2b) and the elastic member (1b) are stacked and adhered onto the other side of the intermediate elastic member (3). The stator (13) is inserted into a hollow portion of the rotor (12). The rotor (12) comprises a pair of friction members (5a, 5b) and a pair of supporting members (4a, 4b). The stator (13) is pinched by the supporting members (4a, 4b). Further the rotor (12) is pressed to the stator (13) by the spring (8) along an axial direction of the spindle (6).
Further, each piezoelectric member (2a, 2b) includes two drive elements. These two drive elements are mutually shifted along the circumferential direction of the piezoelectric members (2a, 2b) with a proper interval corresponding to 1/4 the wave length of the travelling wave. When a pair of A.C. signals with 90.degree. difference in phase are supplied to the piezoelectric member (2a, 2b), a pair of travelling waves are generated on both elastic members (1a, 1b). When the travelling waves are generated, the rotor (12) is rotated according to circulation of the travelling waves.
However, there are no adjusting means for adjusting the pressures which are applied to both sides of the intermediate elastic member (3) in the conventional vibration wave motor. Accordingly, vibration characteristics on opposite sides of the intermediate elastic member (3) can not be harmonized. Therefore, the rotor (3) might generate squealing and the output torque might be reduced.